US10012250B2 - Stress-engineered frangible structures - Google Patents

Abstract

A stress-engineered frangible structure includes multiple discrete glass members interconnected by inter-structure bonds to form a complex structural shape. Each glass member includes strengthened (i.e., by way of stress-engineering) glass material portions that are configured to transmit propagating fracture forces throughout the glass member. Each inter-structure bond includes a bonding member (e.g., glass-frit or adhesive) connected to weaker (e.g., untreated, unstrengthened, etched, or thinner) glass member region(s) disposed on one or both interconnected glass members that function to reliably transfer propagating fracture forces from one glass member to other glass member. An optional trigger mechanism generates an initial fracture force in a first (most-upstream) glass member, and the resulting propagating fracture forces are transferred by way of inter-structure bonds to all downstream glass members. One-way crack propagation is achieved by providing a weaker member region only on the downstream side of each inter-structure bond.

Description

FIELD OF THE INVENTION

This invention relates to frangible structures, and in particular to frangible structures formed using stress-engineered frangible materials.

BACKGROUND OF THE INVENTION

Frangible materials are materials, such as glass, that tend to break up into fragments when subjected to a deforming force or impact, as compared with non-frangible materials that elastically deform and retain cohesion when subjected to comparable deforming forces. The phrase “glass material” refers to any of various amorphous frangible materials formed from a melt by cooling to rigidity without crystallization. The most commonly known glass materials are usually transparent or translucent material consisting typically of a mixture of silicates, but the phrase “glass material” is not limited to silicate-based glass unless otherwise specified.

Frangible structures (i.e., structures formed using one or more frangible materials) are utilized in a wide range of practical applications ranging from small and simple to large and complex. Most frangible structures are designed to undergo structural failure (break away) when struck by an externally applied impact force. For example, light poles or airport lighting structures are designed to break away when hit by a vehicle or plane in order to lessen damage to the vehicle/plane and minimize injury to the passengers. Some frangible structures are designed to undergo structural failure in response to an externally generated command signal. For example, transient electronic devices are frangible structures that include one or more electronic devices (e.g., integrated circuit (IC) chip and/or printed electronic devices) mounted on a stress-engineered glass substrate along with a trigger mechanism. The glass material forming the glass substrate is stress-engineered (e.g., intentionally fabricated using thermally tempered, ion-exchange treated, or lamination techniques) to store potential energy in the form of residual internal stress gradients such that, when the stress-engineered glass substrate is subjected to a relatively small initial fracture force generated by the trigger mechanism, the stored potential energy is released in the form of a propagating fracture force that is quickly transferred throughout the glass substrate.

Currently, there are no known methodologies for producing complex frangible structures that undergo on-command structural failure in response to a single initiating force (i.e., where the single initiating force has an trigger area much smaller than the overall structural area, preferably smaller than 1 μm²). That is, there is no practical way to generate a large complex structure, such as an airplane wing section, from a single (integrally-molded or machined) piece of frangible material. Conversely, when multiple discrete stress-engineered glass structures are adhered together to form the complex shape, propagating fracture forces are unable to transfer from one frangible glass structure to an adjacent frangible glass structure, thereby requiring multiple triggering forces (i.e. one trigger mechanism for each frangible glass structure) to achieve complete structural failure of the entire complex frangible structure.

What is needed is a methodology for generating complex stress-engineered frangible structures that reliably undergoes on-command structural failure in response to a single triggering force with a triggering area much smaller than the structural area.

SUMMARY OF THE INVENTION

The present invention is directed to methods for forming novel inter-structure bonds that function to both structurally connect adjacent discrete glass members, and also to reliably transfer propagating fracture forces between the connected discrete glass members, thereby facilitating the production of complex stress-engineered frangible structures that both exhibit high structural strength during normal operation, and also undergo complete structural failure in response to a single (initial) fracture force during emergency or other operating conditions. Because the method uses separately formed (discrete) glass members that can have any size and shape (e.g., curved shapes, rods, sheets, tubs, or spheres), the method facilitates the production of a wide range of complex stress-engineered frangible structures (i.e., by way of forming the glass members as component structural elements of the assembled complex structure). To facilitate both high structural strength during normal operation and on-command controlled structural failure, each discrete glass member includes a portion that is strengthened by way of stress-engineering to both exhibit enhanced structural strength, and to store potential energy in an amount that transmits propagating fracture forces throughout the glass member in response to a sufficiently large initial fracture force such that the glass member undergoes structural failure (i.e., fracture and/or fragmentation into two or more separate pieces). In alternative embodiments, the strengthened glass portion of each glass member is generated either during formation of the glass member or by treating an already-formed (untreated) glass member using a stress-engineering technique such as thermal tempering, laminating, or ion-exchange treatment. To facilitate both rigid structural connection between adjacent discrete glass members, and also reliable transfer of propagating fracture forces between the connected discrete glass members, each novel inter-structure bond includes a bonding member directly attached to one or more weaker member regions of one or more of the two connected glass members (e.g., with the bonding member connected either between a strengthened glass portion of one glass member and the weaker member region of the other glass member, or between weakened glass portions disposed on both glass members). Because the weaker/weakened glass material of the one or more weaker member regions is more susceptible to fracture (i.e., fractures in response to a lower incident fracture energy), and because the one or more weaker member regions extend into the downstream glass member, the novel inter-structure bonds generated in accordance with the present invention facilitates the reliable transfer of propagating fracture forces from an upstream (first) glass member to an adjacent downstream (second) glass member by way of generating a transfer fracture force, in response to propagating fracture forces in the upstream glass member, that extend into the weaker member region formed in the downstream glass member, thereby generating sufficient fracture energy to produce propagating fracture forces in the downstream glass member. With this basic arrangement, the present invention facilitates reliably generating propagating fracture forces that are sequentially transferred from connected glass member to connected glass member until a desired amount of structural failure is generated in the contiguous complex stress engineered frangible structure. By way of controlling the initial fracture force (e.g., using an optional RF signal controlled trigger mechanism), the present invention thus provides a new class of functional complex frangible structures that disintegrate, lose mass, or otherwise undergo structural failure on command, whether for the safety to an impacting object (e.g., in the case of light poles or airport structures), or to control functionality (e.g., to optimize the trim of a wing or propeller used on an aircraft).

According to an embodiment of the invention, a complex stress-engineered frangible structure capable of on-command structural failure is at least partially produced by assembling “core” structural elements including two (first and second) discrete glass members that are directly connected by way of an intervening inter-structure bond, and an optional trigger mechanism directly connected to the first glass member. As mentioned above, the glass members are separately formed (integral) glass pieces substantially made up of strengthened (stress-engineered) glass portions. The intervening inter-structure bond includes a bonding member sandwiched between opposing surface regions of the first and second glass members, and the optional trigger mechanism is operably attached to an associated surface region of the first glass member. The trigger mechanism is configured to generate, in response to a trigger signal, an initial fracture force in a localized region (point) in the first glass member, thereby producing an initial (first) propagating fracture force in the first glass member that propagates (travels) by way of the strengthened glass material portion to all sections of the first glass member, eventually reaching the surface region of the first glass member to which intervening bonding member is attached. When the initial propagating fracture force is transmitted to the bonding member, the one or more weaker member regions and the bonding member combine to generate a transfer fracture force that passes from the strengthened glass portion of the first (upstream) glass member to the strengthened glass portion of the second (downstream) glass member, where the transfer fracture force has sufficient strength to initiate secondary propagating fracture forces in the second glass member. By extending this methodology to generate complex stress-engineered frangible structures having a large number of additional discrete glass members connected directly or indirectly (i.e., through one or more intervening glass members) by way of associated inter-structure bonds to the first glass member, the single initial fracture force generated by the trigger mechanism is reliably utilized to fragment every glass member forming the contiguous complex frangible structure. Accordingly, the present invention facilitates the production of a wide range of complex stress-engineered frangible structure configurations that undergo on-command structural failure by way of incorporating the “core” elements mentioned above (i.e., the first and second glass members, at least one inter-structure bond, and the trigger mechanism).

According to an exemplary practical approach, complex stress-engineered frangible structures are produced by way of generating a weaker member region in at least one of the upstream and downstream glass members, and then connecting each upstream and downstream glass member pair such that a bonding member (e.g., ceramic adhesive, low temperature glass frit, anodic bonding structures, or chemical bonds) is sandwiched between the upstream and downstream glass members, and such that the bonding member presses against and covers the weaker member region(s). In alternative embodiments, the weaker member region is implemented by weakened glass portions (i.e., localized glass portions that are protected from ion-exchange or other stress-engineering treatment), by weakened surface features (i.e., sections of the glass surface that are etched, laser ablated or otherwise weakened by way of removing glass material from the second glass member through a designated surface region), or by being disposed on a thinner (and thus weaker) section of stress-engineered glass material. The upstream and downstream glass members are then connecting by way of the inter-structure bonds mentioned above such that each bonding member is connected between an associated surface region of an upstream glass member and associated weaker member region of a corresponding downstream glass member (i.e., such that the surface region contacted by the bonding members entirely surrounds/covers the weaker member region). In the specific embodiment involving weakened glass portions, the second glass member is provided by way of procuring or fabricating an untreated (i.e., non-stress-engineered) glass member, masking a designated surface region of the untreated glass member, ion-exchange treating all exposed surfaces the untreated glass member to convert the second glass member into a stress-engineered glass member including the weakened glass portion disposed under the mask, and then removing the mask. In the specific embodiment involving weakened surface features, the second glass member is subjected to stress-engineering, and then features are etched or otherwise formed in the strengthened glass material to form the weakened surface feature. In alternative exemplary embodiments, the weakened surface feature are defined as a single (e.g., square) cavity, an array of cavities formed in a waffle-type pattern, or parallel slots. In each case, the removed untreated material generates a localized weakened region in the downstream glass member that greatly facilitates transfer of propagating fracture forces from the upstream glass member to the downstream glass member.

According to another practical approach, complex stress-engineered frangible structures are produced by way of procuring, fabricating or otherwise providing glass members in an untreated (i.e., non-stress-engineered) state, connecting the glass members using high temperature glass bonding techniques (e.g., high-temperature glass-frit or glass welding) such that a bonding member is connected between opposing surface regions of the glass members, and then subjecting exposed portions of the untreated glass members to an ion-exchange treatment to form stress-engineered glass members connected by an inter-structure bond. In this case, the inter-structure bond includes the bonding member and two weakened glass portions (member regions) that are respectively formed on opposite sides of the bonding member by portions of the two glass members that are shielded during ion-exchange treatment. To avoid structural problems caused by high-temperature bonding, the discrete untreated glass members are respectively formed from glass materials having the same or similar CTE values. In one embodiment, channels are formed in exposed surface portions of the untreated glass members prior to ion-exchange treatment.

According to another embodiment of the present invention, a method is provided for producing a complex frangible structure in which propagating fracture forces are transferrable in only one direction (i.e., only from upstream glass members to downstream glass members, and not in the reverse direction). This feature is useful, for example, when one part of a structure needs to be intact but still structurally bonded to the overall complex structure. Any accidental breakage of the other parts will not affect the structure that needs to stay intact until the very end. This method will ensure a particular user sequence of fracturing will occur in a multi-triggerable system. The method involves producing all glass members in the manner described above such that the glass members are sized and shaped to collectively form a complex frangible structure, with one glass member designated as a first (most-upstream) glass member, one or more glass members designated as the last (most-downstream) glass member(s), and all other glass members designated as intermediate glass members that are downstream to the first glass member and upstream to the last glass member(s). Bonding regions are designated between adjacent associated upstream/downstream pairs of the glass members such that a fracture path is defined from the first glass member to the last glass member(s) by way of any intervening intermediate glass members and inter-structure bonds. To facilitate one-way crack propagation, the weaker member regions (i.e., weakened surface features and/or weakened glass portions) are formed only on the downstream side of each bonding region (i.e., only on the downstream glass member of each associated upstream/downstream glass member pair). The glass members are then interconnected by way of forming inter-structure bonds in the manner described above such that each bonding member is disposed between a strengthened glass portion of the upstream glass member and the weaker member region of the downstream glass member. A trigger mechanism is also connected to the first glass member, either before, during or after the bonding process. The resulting complex frangible structure thus exhibits one-way propagating fracture forces that are initiating in the first glass member by the trigger mechanism, and are sequentially transferred in only one direction (i.e., only from upstream to downstream glass members of each connected upstream/downstream pair) until the fracture forces reach the last glass member(s).

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings, where:

FIG. 1 is a top side perspective view showing a complex stress-engineered frangible structure according to a simplified embodiment of the present invention;

FIG. 2 is a flow diagram showing a generalized method for producing the complex stress-engineered frangible structure ofFIG. 1;

FIG. 3 is a flow diagram depicting an After Ion-Exchange Treatment approach for producing complex stress-engineered frangible structures according to a first practical embodiment;

FIGS. 4(A),4(B1),4(B2),4(C1),4(C2),4(D1),4(D2),4(E),4(F),4(G),4(H) and4(I) are simplified cross-sectional side views depicting the After Ion-Exchange Treatment approach ofFIG. 3;

FIGS. 5(A), 5(B), 5(C) and5(d) are partial perspective views showing weaker member regions generated during the After Ion-Exchange Treatment approach ofFIG. 3 according to alternative exemplary specific embodiments;

FIG. 6 is a flow diagram showing a Before Ion-Exchange Treatment approach for producing complex stress-engineered frangible structures according to a second practical embodiment;

FIGS. 7(A), 7(B), 7(C), 7(D), 7(E), 7(F), 7(G) and 7(H) are simplified cross-sectional side views depicting the Before Ion-Exchange Treatment approach ofFIG. 6; and

FIG. 8 is a flow diagram showing a method for producing complex stress-engineered frangible structures exhibiting one-way crack propagation according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention relates to an improvement in frangible structures. The following description is presented to enable one of ordinary skill in the art to make and use the invention as provided in the context of a particular application and its requirements. As used herein, directional terms such as “upper”, “upward”, “lower”, “downward”, “under” and “over” are intended to provide relative positions for purposes of description, and are not intended to designate an absolute frame of reference. The terms “coupled” and “connected”, which are utilized herein, are defined as follows. The term “connected” is used to describe a direct connection between two structural elements, for example, by way of an adhesive or other bonding member. In contrast, the term “coupled” is used to describe either a direct connection or an indirect connection between two structural elements. For example, two coupled elements may be directly connected by way of a bond, or indirectly connected by way of an intervening structural element. The term “integral” is used to refer to a structural element (such as a glass member or piece) that is entirely separately produced by way of molding or machining a single material piece. Various modifications to the preferred embodiment will be apparent to those with skill in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed.

FIG. 1 includes simplified perspective views showing a complex stress-engineeredfrangible structure100 in a contiguous state (i.e., frangible structure100(t0) shown in the middle portion ofFIG. 1) and an exemplary fractured state (i.e., frangible structure100(t2) shown in the lower portion ofFIG. 1). In the contiguous state (e.g., immediately after production, during normal operation, and during portions of a transient event occurring prior to fracture), frangible structure100(t0) generally includes two discrete glass members110-1 and110-2, aninter-structure bond120 and anoptional trigger mechanism130.

As utilized herein, the phrase “discrete glass member” refers to a separate (integral) glass pieces formed using known techniques (i.e., heating the glass material to a molten state, forming the molten glass into a desired final shape, and then cooling the molten glass to room temperature). An advantage to forming complex stress-engineeredfrangible structure100 using discrete glass members110-1 and110-2 is that combining and bonding discrete glass members facilitates the production of complex structural shapes far more efficiently and with less expense than forming the same complex structural shape from a single integral glass piece.

In order to producefrangible structure100 such that it both provides sufficient structural strength during normal operation and also undergoes on-command fragmentation (structural failure), it is necessary to fabricate or procure stress-engineered glass members having the characteristics set forth below. Referring to the middle ofFIG. 1, glass members110-1 and110-2 are depicted as wafer-like structures having opposing upper and lower surfaces112-1 and112-2 and113-1 and113-2, respectively, but in practice glass members110-1 and110-2 can have any practical shape (e.g., curved shapes, rods, sheets, tubs, or spheres). Glass members110-1 and110-2 are separately formed (integral) glass pieces mostly comprising strengthened glass portions111-11S and111-21S, respectively, where strengthened glass portions111-11S and111-21S comprise glass material that has been fabricated or treated using a known stress-engineering technique such as thermal tempering, laminating, or ion-exchange treatment such that strengthened glass portions111-11S and111-21S both exhibits substantially higher structural strength than non-stress-engineered glass material of the same type, and stores potential energy in a sufficient amount to generate the propagating fracture forces described below. In a presently preferred embodiment, strengthened glass portions111-11S and111-21S of glass members110-1 and110-2 comprise ion-exchange treated glass material formed using known techniques. In another exemplary embodiment, as indicated in the upper left bubble ofFIG. 1, glass members110-1 and110-2 comprise two interspersed thermally tempered glass materials (e.g., with multiple thermally tempered glass material portions111-S21,111-S22 and111-S23 disposed in a different (first) thermally tempered glass material111-S1. When implemented using ion-exchange treatment or any of the other specific stress-engineering processes mentioned above, glass members110-1 and110-2 are configured to contain enough stored potential energy to generate self-propagating secondary fracture forces in response to an initial fracture force such that, as depicted by shattered structure100(t2) at the bottom ofFIG. 1), glass members110-1 and110-2 partially or completely break apart into smaller fragments using a mechanism similar to that captured in a Prince Rupert's Drop. In addition, in one embodiment, the released potential energy also fractures portions ofoptional trigger mechanism130 and any other structures that might be disposed on glass members110-1 and110-2.

As indicated inFIG. 1,inter-structure bond120 functions to fixedly connect (bond) lower (first) glass member110-1 to upper (second) glass member110-2 by way of a bonding member125 (sandwiched) between an upward-facing surface region113-11 of first glass member110-1 and an opposing downward-facing surface region112-21 of second glass member110-2. In alternative exemplary embodiments,bonding member125 is implemented using a ceramic adhesive, a glass-frit structure, an anodic bonding structure, or a chemical bond.

In one embodiment,trigger mechanism130 is attached to a second surface region113-12 of first glass member110-1, and is configured to generate an initial fracture force F₀in glass member110-1 having sufficient fracture energy to initiate first propagating fracture force F_p1in strengthened portion111-11S of first glass member110-1. In a specific embodiment, trigger mechanism is controlled by way of an electronic trigger signal TS generated by asensor160, which in turn generates trigger signal TS in response to a wireless transmitted wave signal (e.g., a light wave signal, a radio frequency, or an acoustic/sound signal, not shown), wherebyfrangible structure100 can be remotely actuated to undergo on-command structural failure. In one embodiment,trigger mechanism130 generates initial fracture force F₀using a self-limiting resistive element and a switch element that are connected in series between a battery (or other DC power source) and ground in the manner described in co-owned and co-pending application Ser. No. 15/220,164, filed Jul. 26, 2016, which is incorporated herein by reference in its entirety.

According to an aspect of the present invention,bonding member125 ofinter-structure bond120 is directly attached to at least one weaker member region of at least one of glass members110-1 and110-2. Referring to the lower right bubble inFIG. 1, a glass portion111-12M of glass member110-1 is depicted by the dashed-line box disposed directly belowbonding member125, and glass portion111-22M of glass member110-2 is depicted by the dashed-line box disposed directly abovebonding member125. Note that glass portion111-12M is contiguous with upper surface region113-11 of first glass member110-1, and that glass portion111-22M is contiguous with lower surface region112-21 of first glass member110-1. According to this aspect, at least one of the two glass portions111-12M and111-22M comprises a weaker member region (i.e., glass material that is, e.g., either subjected to mechanical alteration or shielded from stress-engineering such that the glass material is structurally weaker than the stress-engineered glass material forming strengthened portions111-11S and111-21S). For example, in one exemplary alternative embodiment, all three of strengthened portions111-11S and111-21S and glass portions111-12M comprise ion-exchange treated glass material (i.e., stress-engineered, relatively thick glass material), and glass portion111-22M comprises the weaker member region (e.g., glass material that is partially or fully shielded from ion-exchange treatment, glass material that has been mechanically weakened, e.g., by way of etching, or relatively thin stress-engineered glass material). Alternatively, all three of strengthened portions111-11S and111-21S and glass portion111-22M comprise strengthened (e.g., ion-exchange treated) glass material, and glass portion111-12M comprises the weaker member region. In a third example, strengthened portions111-11S and111-21S comprise stress-engineered glass material, and both glass portions111-12M and111-22M comprise weaker member regions. Detailed examples used to form weaker member regions are provided below.

According to another aspect of the present invention,bonding member125 and the weaker member region(s) (i.e., either or both of glass portions111-12M and11122M) are configured (i.e., operably formed and positioned) to transfer propagating fracture forces F_P1from first glass member110-1 to second glass member110-2 by way of a transfer fracture force F_F1such that secondary propagating fracture forces F_P2are generated in strengthened glass portion111-21S of second glass member110-2. That is, as depicted in the lower right bubble inFIG. 1, the weaker member region(s) andbonding member125 produce transfer fracture force F_F1, which is applied in localized region111-21SL of strengthened portion111-21S of glass member110-2, thereby generating secondary propagating fracture forces F_P2in strengthened portion111-21S of glass member110-2. Although not illustrated inFIG. 1, secondary propagating fracture forces F_P2travel throughout second glass member110-2 such that glass member110-2 is fragmented. In this way, initial fracture force F_F0generated in first glass member110-1 bytrigger mechanism130 results in structural failure of second glass member110-2 by way of secondary propagating fracture forces F_P2. The inventors found that forminginter-structure bond120 with one or more weaker member regions adjacent tobonding member125 greatly facilitates the transfer of propagating fracture forces between two discrete glass members because the weakened glass material of the weaker member region(s) more reliably fractures in response to relatively weak transferred fracture forces. Moreover, by limiting the weaker/weakened glass material to the region immediately adjacent thebonding member125, the present invention facilitates the transfer of fracture forces between adjacent members without significantly weakening contiguous complex stress-engineeredfrangible structure100.

FIG. 2 is a flow diagram showing a generalized method for producing complex stress-engineered frangible structures. For brevity, the generalized method is described with reference to the production of the simplified, two-member frangible structure shown inFIG. 1, although those skilled in the art will understand that the described methodology is extendable to form complex stress-engineered frangible structures having any desired shape, size and number of glass elements. The block numbers mentioned below refer to the blocks shown inFIG. 2, and element numbers mentioned below refer to corresponding structures shown inFIG. 1.

Referring to the top ofFIG. 2, block205 involves providing (i.e., fabricating or procuring) discrete glass members having required associated sizes and shapes such that, when operably assembled and interconnected, the provided glass members implement component structural elements that collectively form the complex structural shape of a desired complex stress-engineered frangible structure. Using the simplified embodiment ofFIG. 1, providing the glass members involves separately fabricating glass members110-1 and110-2 using either normal glass forming techniques or stress-engineering glass fabrication techniques. According to an embodiment of the present invention, providing the discrete glass members includes producing the glass members using normal glass forming techniques (i.e., such that all of the glass material of each glass member is in an untreated state, i.e., not yet stress-engineered).

Block210 ofFIG. 2 involves processing and assembling (interconnecting) the component glass members using the novel inter-structure bonds described herein to form the desired complex frangible structure. Usingfrangible structure100 ofFIG. 1 as a simplified example, glass members110-1 and110-2 are processed and directly connected usinginter-structure bond120 to glass member110-2 such thatbonding member125 contacts at least one weaker member region as described above. Note that, once operably processed and connected, glass members110-1 and110-2 andinter-structure bond120 are configured to transfer first propagating fracture forces F_P1from strengthened portion111-11S of glass member110-1 to strengthened portion111-21S of glass member110-2 such that secondary propagating fracture forces F_P2are generated in glass member110-2 in response to transfer fracture force F_F1.

Referring to the lower portion ofFIG. 2, block220 includes an optional process involving mounting a trigger mechanism onto one of the glass members using known techniques. Using the simplified example ofFIG. 1, this process involves mountingtrigger mechanism130 onto upper surface region113-12 of first glass member110-1 using a suitable adhesive or other mechanism such that initial fracture force F_F1is operably transferred into glass member110-1. In alternative embodiments,trigger mechanism130 is mounted onto glass member110-1 either before or after glass member110-1 is connected to glass member110-2 by way of inter-structure bond120 (i.e., unless otherwise specified, block220 may be performed before or during block210).

According to alternative specific embodiments, the generalized production method ofFIG. 2 is presented below in additional detail with reference to two alternative approaches. An “After Ion-Exchange Bonding” approach is described below with reference toFIGS. 3, 4(A) to4(I), and5(A) to5(D), and generally involves bonding discrete glass members after the glass members have been subjected to ion-exchange-type stress-engineering treatment treated to patterned stress-engineering treatment. A “Before Ion-Exchange Bonding” approach is then described with reference toFIGS. 6 and 7(A) to7(G), and generally involves bonding discrete glass members before subjecting the glass members to ion-exchange-type stress-engineering treatment. These two exemplary methods represent currently preferred practical methodologies for implementing the generalized production method ofFIG. 2, but are not intended to be limiting unless otherwise specified in the claims.

Referring toFIG. 3, the procuring/fabricating and assembly (blocks205 and210,FIG. 2) portion of the generalized production method according to the After Ion-Exchange Bonding approach generally includes forming a weaker member region in each downstream (second)glass member110A-2, and then connecting upstream (first)glass member110A-1 to downstream glass member such that a bonding member is sandwiched between the upstream and downstream glass members and presses against and covers the weaker member region(s). The After Ion-Exchange Bonding approach is described with reference to two alternative exemplary practical embodiments: a first practicalembodiment including blocks205A,312,313,314A and315 involving the generation of a weaker member region in the form of a weakened glass region, and a second practicalembodiment including blocks205A,312,313,314A and315 involving the generation of a weaker member region in the form of a weakened surface feature. Because the overall process flow of these alternative practical embodiments is substantially the same, the weakened glass region embodiment process (i.e., blocks205A,312,313,314A and315 ofFIG. 3) will be described with reference toFIGS. 4(A),4(B1),4(C1),4(D1) and4(E), and the weakened surface feature embodiment process (i.e., blocks205A,313,314B and315 ofFIG. 3) will be described with reference toFIGS. 4(A),4(B2),4(C2),4(D2) and4(E). Note thatFIGS. 4(A) to 4(F) which depict upstream and downstream glass members and associated features in simplified side view.

Referring to block205A (FIG. 3) and toFIG. 4(A), the “After Ion-Exchange Bonding” production method approach begins with procuring or fabricating (providing) untreated (i.e., non-stress-engineered)glass members110A-1A and110A-2A (i.e., such thatglass member110A-1A entirely comprises “weakened” (untreated)glass material111A-1, andglass member110A-2A entirely comprises “weakened”glass material111A-2). According to an aspect of the present embodiment,untreated glass members110A-1A and110A-2A can have varying thicknesses (e.g., thickness T_110A-1Aofglass member110A-1A can be different from thickness T_110A-2Aofglass member110A-2A) because propagating fracture forces (cracks) only occur at a surface of each member.

Block312 and toFIG. 4(B1) are associated with the weakened glass portion embodiment, and involve forming a mask410 (e.g., photoresist or other material) over a designatedsurface region112A-21 ofuntreated glass member110A-2A (i.e., over a region ofglass member110A-2A that is designated for weakening). As depicted inFIG. 4(B1), designatedsurface region112A-21 to whichmask410 is applied is located under an untreated (and thus “weakened”)glass portion111A-21W ofglass member110A-2A. The shape/pattern ofmask410 is determined by the weakened surface feature pattern to be formed inglass member110A-2A. Note that no processing ofglass member110A-1A occurs at this time. Note also, as shown inFIG. 4(B2), that no mask is formed in conjunction with the weakened surface feature embodiment at this time.

Referring to block313 (FIG. 3) and toFIGS. 4(C1) and4(C2), all exposed surfaces of bothuntreated glass members110A-1A and110A-2A are then subjected to ion-exchange treatment, thereby converting the unprocessed glass members in to stress-engineeredglass members110A-1 and110A-2 (i.e., having features consistent with glass members110-1 and110-2 ofFIG. 1). Referring toFIG. 4(C1), according to the weakened glass portion approach, note that the entireupper surface113A-2 and exposed portions oflower surface112A-2 are fully ion-exchange treated, but mask410 limits or entirely prevents ion-exchange treatment from entering weakenedglass portion111A-21A throughmasked surface region112A-21A, wherebyglass member110A-2 is processed to include a large strengthenedglass portion111A-22S and a relative small weakenedglass portion111A-21A. In contrast, all regions ofupper surface113A-1 andlower surface112A-1 ofglass member110A-1 are subjected to ion-exchange treatment. Note also that generating weakenedglass portion111A-21A only onglass member110A-2 produces a one-way crack propagation bond (i.e., cracks must propagate fromglass member110A-1 toglass member110A-2). In an alternative embodiment, both sides of the bonded area are masked and weakened. For example, as indicated inFIG. 4(C1), acorresponding region111A-11 ofglass member110A-1 can be subjected to masking and similarly weakened, which would result in two-way crack propagation. Note also that the surface area of weakenedglass portion111A-21A is always smaller than the bonded area. Referring toFIG. 4(C2), in the weakened surface feature embodiment, because both untreated glass members are entirely exposed, all surfaces112A-1,113A-1,112A-2 and113A-2 are subjected to ion-exchange treatment, thereby producing stress-engineeredglass members110A-1 and110A-2 substantially entirely made up of strengthenedglass material111A-12S and111A-22S (i.e., designatedbonding regions111A-21S and111A-11S both comprise strengthened glass).

Referring to block314A (FIG. 3) and toFIG. 4(D1), the last step of the weakened glass portion approach involves removingmask410 fromglass member110A-2, thereby exposing designatedbonding surface region112A-21A ofglass member111A-2.FIG. 5(A) depicts an exemplary portion of aglass member110A-21 indicating an exemplary weakenedglass region111A-21W disposed within designatedsurface region112A-22, and indicates that the designatedbonding surface region112A-21 against which the bonding member will be pressed entirely surroundssurface region112A-22. Referring again toFIG. 4(D1), note also thatglass member111A-2 now includes relatively small weakened glass portion (member region)111A-21W and relatively large strengthenedglass portion111A-22S. Note also that the corresponding designatedbonding region111A-11 ofglass member111A-1 is strengthened (i.e., stress-engineered using the same process as that used to form strengthenedglass portion111A-21).

Referring to block314B (FIG. 3) and toFIG. 4(D2), the next step of the weakened surface feature embodiment involves forming weakenedsurface feature111A-21F inglass member110A-2 by way of removing glass material from strengthenedportion111A-21S through designatedsurface region112A-22. In one specific embodiment, this glass removal process is achieved by etching (i.e., applying asuitable chemical etchant420 using known techniques) designatedsurface region112A-22 to define one or more cavities inglass member110A-2.FIGS. 5(B) to 5(D) depict simplified exemplary weakened surface features111A-21F1 to111A-21F3.FIG. 5(B) depicts a single (e.g., square) cavity weakened surface features111A-21F1 etched throughsurface region112A-21 oflower surface112A-2 of aglass member110A-22 entirely within designatedbonding surface region112A-21.FIG. 5(C) depicts a second weakenedsurface feature111A-21F2 including multiple adjacent cavities arranged in a checkerboard or waffle-type pattern that are etched throughsurface region112A-21 oflower surface112A-2 ofglass member110A-22 and entirely within designatedbonding surface region112A-21).FIG. 5(D) depicts a third (slot or line-type) weakenedsurface feature111A-21F3 etched throughsurface region112A-21lower surface112A-2 ofglass member110A-23 and entirely designatedbonding surface region112A-21). The size of weakened surface features111A-21F1 to111A-21F3 is determined by the glass materials and other conditions, and the inventors presently believe that features occupying surface regions as small as 1 μm by 1 μm may be utilized.

Referring to block315 (FIG. 3) and toFIG. 4(E), the first glass member11A-1 is then connected tosecond glass member110A-2 using abonding member125A and an associated low-temperature (i.e., less than 400° C.) bonding technique, thereby completingbond120A includingbonding member125A andweaker member region111A-21M (i.e., one of weakenedglass portion111A-21W or weakened surface features111A-21F, which are transposed inFIG. 4(E) for illustrative purposes). In alternative specific embodiments, connectingglass members110A-1 and110A-2 includes utilizing one of a ceramic adhesive, a low temperature glass-frit, an anodic bonding structure, and a chemical bond to formbonding member125A. Note that width W22 ofcontact surface region112A-22 that is contacted byglass member125A is larger than width W21 of designatedsurface region112A-21, which defines the width ofweaker member region111A-21M. That is, as indicated in additional detail inFIGS. 5(A) to 5(D), in each instance the area ofcontact surface region112A-22 entirely surrounds weakenedglass portion111A-21W and weakened surface features111A-21F1 to11A-21F3. Depending on bonding temperature,glass members110A-1 and110A-2 may be formed using glass materials having different coefficient of thermal expansion (CTE) values (i.e., the lower the bonding process temperature, the greater the difference in CTE between the two glass members).

Referring again to the bottom ofFIG. 3 and toFIG. 4(F), subsequent production processing includes mounting (operably attaching) trigger mechanism onto acorresponding surface region113A-12 ofupper surface113A-1 onglass member110A-1, thereby completing the production of complex stress-engineeredfrangible structure100A according to the “After Ion-Exchange Bonding” approach. Note thatfrangible structure100A is characterized byweaker member region111A-21M disposed onsecond glass member110A-2, and thatbonding member125A is sandwiched betweensurface region113A-21 ofglass member110A-1 andcorresponding surface region112A-21 ofglass member110A-2, where the bondedsurface region112A-21 entirely surroundsweaker member region111A-21M, as discussed above with reference toFIGS. 5(A) to 5(D). In effect,bonding member125A is connected betweenweaker member region111A-21M ofdownstream glass member111A-2 and strengthenedglass portion111A-11S ofupstream glass member111A-1. In this state, complex stress-engineeredfrangible structure100A is ready to deploy.

FIGS. 4(G) to 4(I) depict a simplified structural failure of complex stress-engineeredfrangible structure100A by way of a one-way crack (fracture) propagation pattern. Referring toFIG. 4(G), a time (t0) represents a moment that on-command structural failure offrangible structure100A is desired, and is initiated by way of applying trigger signal TS to triggermechanism130A. As explained above,trigger mechanism130A is configured to generate an initial fracture force F_F0in response to trigger signal TS, where initial fracture force F_F0has sufficient energy to generate a first propagating fracture force F_P1in strengthenedportion111A-12S ofglass member110A-1. Note that that, at time t0, first propagating fracture force F_P1has not yet reachedinter-structure bond120A, soglass member110A-2 remains entirely intact and un-fractured.FIG. 4(H) showsfrangible structure100A at a subsequent time (t1) when propagating fracture force F_P1has traveled throughoutglass member110A-1 and reachedinter-structure bond120A. As described above,bonding member125A andweaker member region111A-21M (which includes, e.g., either weakenedglass portion111A-21W shown inFIG. 4(D1) or weakenedsurface feature111A-21F shown inFIG. 4(D2)) are configured to transfer first propagating fracture forces F_P1by way of secondary fracture force F_F1fromglass member110A-1adjacent glass member110A-2 such that secondary propagating fracture forces F_P2are generated in strengthenedglass portion111A-21S ofglass member110A-2.FIG. 4(I) showsfrangible structure100A at a subsequent time (t2) when secondary propagating fracture forces F_P2propagate throughglass member110B-2, whereby a single initial fracture force F_F0generated inglass member110A-1 bytrigger mechanism130A results in structural failure ofsecond glass member110A-2.

The “Before Ion-Exchange Bonding” production method approach and subsequent on-command structural failure will now be described with reference toFIG. 6 and toFIGS. 7(A) to 7(H).

Referring to block205B (FIG. 6) and toFIG. 7(A), the “Before Ion-Exchange Bonding” production method approach begins with procuring or fabricating (providing) untreated (i.e., non-stress-engineered)glass members110B-1A and110B-2A (i.e.,glass members110B-1A and110B-2A entirely comprise “weakened” (untreated)glass material111B-1 and111B-2, respectively). According to an aspect of the “Before Ion-Exchange Bonding” approach,untreated glass members110B-1A and110B-2A preferably have similar thicknesses (i.e., thickness T_110B-1Aofglass member110B-1A is substantially equal to thickness T_110B-2Aofglass member110B-2A) in order to avoid CTE related issues associated with high-temperature bonding and subsequent processing. However, the component member thicknesses may be varied is some instances to vary the fracturing and strength properties of the contiguous frangible structure.

Referring to block612 and toFIG. 7(B), aninter-structure bond120B is formed by connecting a designatedsurface bonding region113B-11 onupper surface113B-1 ofglass member110B-1A to an opposing designatedsurface region112B-21 onlower surface112B-2 ofglass member110B-2A by way of an interveningglass bonding member125B (e.g., a high-temperature glass-frit structure, or a glass welding structure). In this case,inter-structure bond120B includesglass bonding member125B, a first weakenedglass portion111B-11W disposed inuntreated glass member110B-1A adjacent to designatedsurface region113B-11, and a second weakenedglass portion111B-21W disposed inuntreated glass member110B-2A adjacent to designatedsurface region112B-21. These regions are designated by dashed lines inFIG. 7(B) to indicate that these regions remain contiguous with the remaining untreated glass material forminguntreated glass members111B-1A and111B-2A. Note that weakenedglass portions111B-11W and111B-21W become the weaker member regions of the to-be-completed inter-structure bond.

Referring toblocks613 and614 and toFIGS. 7(C) and 7(D), exposed portions ofuntreated glass members110B-1A and110B-2A are then exposed to an ion-exchange treatment such thatuntreated glass members110B-1A and110B-2A are converted into stress-engineeredglass members110B-1 and110B-2, respectively, that are connected byinter-structure bond120B. Referring to block613 and toFIG. 7(C), in one embodiment channels are formed in exposed surface portions ofuntreated glass members110B-1A and110B-2A using a suitablechannel forming process710. Note that the channels are formed so as not to allow ion-exchange treatment of weakenedglass portions111B-11W and111B-21W. Referring to block614 andFIG. 7(D),glass members110B-1 and110B-2 are then exposed to ion-exchange treatment, where the channels mentioned above facilitate treatment of all desired surfaces in the chemical bath, and provide paths for the chemical to be drained and rinsed fromglass members110B-1 and110B-2 after being pulled out of the bath.

Referring again to the bottom ofFIG. 6 and toFIG. 7(E), subsequent production processing includes mounting (operably attaching)trigger mechanism130B onto a corresponding surface region onupper surface113B-1 ofglass member110B-1, thereby completing the production of complex stress-engineeredfrangible structure100B according to the “Before Ion-Exchange Bonding” approach. Note thatfrangible structure100B is characterized in thatinter-structure bond120B includes weakened glass portions (member regions)111B-11W and111B-21W disposedglass members110B-1 and110B-2, respectively, andbonding member125B sandwiched between opposingsurface regions113B-11 and112B-21 ofglass members110B-1 and110B-2, respectively. At this point complex stress-engineeredfrangible structure100B is ready to deploy.

FIGS. 7(F) to 7(H) depict a simulated on-command structural failure of complex stress-engineeredfrangible structure100B according to an exemplary embodiment. Referring toFIG. 7(F), at time t(0) the on-command structural failure offrangible structure100B is initiated by way of actuatingtrigger mechanism130B to generate an initial fracture force F_F0, which in turn generates first propagating fracture force F_P1inglass member110B-1.FIG. 7(G) showsfrangible structure100B at a subsequent time (t1) when propagating fracture force F_P1has traveled throughoutglass member110B-1 and reachedinter-structure bond120B. As described above,bonding member125B and weakened glass portions (member regions)111B-11W and111B-21W are configured to transfer first propagating fracture forces F_P1by way of secondary fracture force F_F1fromglass member110B-1adjacent glass member110B-2 such that secondary propagating fracture forces F_P2are generated in strengthenedglass portion111B-22S ofglass member110A-2.FIG. 7(H) showsfrangible structure100B at a subsequent time (t2) when secondary propagating fracture forces F_P2propagate throughglass member110B-2, whereby structural failure offrangible structure100B is achieved.

FIG. 8 is a flow diagram showing a method for producing complex stress-engineered frangible structures in which propagating fracture forces are transferrable in only one direction. The method utilizes processes similar to those described above with reference toFIGS. 4(A) to 4(I), and therefore the method will be described with reference to those figures.

Referring to block811 inFIG. 8 and toFIG. 4(A), the method begins by producing glass members (e.g.,glass members110A-1 and110A-2) in the manner described above such that the glass members are sized and shaped to collectively form a desired complexfrangible structure100A. In the case of multiple glass members, one glass member (e.g.,glass member110A-1) is designated as a first (most-upstream) glass member, one or more glass members (e.g.,glass member110A-2) is designated as the last (most-downstream) glass member(s)110A-2, and all other glass members (not shown inFIG. 4(A)) are designated as intermediate glass members that are downstream to the first glass member (and any other preceding glass members in the crack propagation path) and upstream to the last glass member(s) (and any other subsequent glass members in the crack propagation path). Bonding regions (e.g., referring toFIG. 4(B1),surface regions113A-11 and112A-21 ofglass members110A-1 and110A-2, respectively) are designated between adjacent associated upstream/downstream pairs of the glass members such that a fracture path is defined from the first glass member to the last glass member(s) by way of any intervening intermediate glass members and inter-structure bonds (e.g., in the simplified case of two glass members, fromglass member110A-1 toglass member110A-2 by way ofinter-structure bond120A). To facilitate one-way crack propagation, weaker member regions (e.g., either weakenedsurface region111A-21W shown inFIG. 4(D1) or weakenedsurface feature111A-21F shown inFIG. 4(D2)) are formed only on the downstream side of each bonding region (i.e., only ondownstream glass member110A-2 of the associated upstream/downstream glass member pair comprisingglass members110A-1 and110A-2).

Referring to block812 (FIG. 8) and toFIGS. 4(E) and 4(F), the glass members are then interconnected by way of forming inter-structure bonds in the manner described above such that each bonding member (e.g.,bonding member125A inFIGS. 4(E) and 4(F)) is disposed between a strengthened glass portion of the upstream glass member (e.g.,portion111A-11S ofglass member110A-1, shown inFIG. 4(E)) andweaker member region111A-21M ofdownstream glass member110A-2.

Referring to block812 (FIG. 8) and toFIG. 4(F), a trigger mechanism (e.g.,mechanism130A) is also connected to the first glass member (i.e.,glass member110A-1), which is depicted as occurring after the bonding process, but may alternatively occur either before or at any time during the bonding process.

The resulting complex frangible structure, which in a simplified form is generallyconsistent structure100A ofFIG. 4(F), exhibits one-way crack propagation in which propagating fracture forces can only be transferred from upstream glass members to downstream glass members, and not in the opposite direction. For example, referring toFIGS. 4(G) to 4(I), propagating fracture forces F_P1initiated infirst glass member110A-1 (upstream side) bytrigger mechanism130A are transferred in a downstream direction fromupstream glass member110A-1 todownstream glass member110A-2 (downstream side) by way ofinter-structure bond120A. In contrast, if a propagating fracture force is unintentionally initiated indownstream glass member110A-2 (e.g., due to inadvertent impact by a flying rock), the one-way crack propagation approach would prevent transfer of propagating fracture forces fromglass member110A-2 toupstream glass member110A-1.

Although the present invention has been described with respect to certain specific embodiments, it will be clear to those skilled in the art that the inventive features of the present invention are applicable to other embodiments as well, all of which are intended to fall within the scope of the present invention. For example, although the exemplary embodiments show complex stress-engineered frangible structures comprising only two glass members, the various features and aspects of the invention set forth above can be used to produce complex stress-engineered frangible structures having any number of interconnected discrete glass members. Moreover, although the exemplary embodiments depict only a single inter-structure bond connecting two discrete glass members, any number of inter-structure bonds may be utilized to connect two discrete glass members, although the use of a single fracture transfer point is presently preferred. Further, other bonding methods (e.g., adhesives) may be used in combination with the disclosed inter-structure bonds to further strengthen the contiguous complex stress-engineered frangible structure.

Claims (20)

The invention claimed is:

1. A stress-engineered frangible structure comprising:

a plurality of interconnected discrete glass members including a first glass member and a second glass member, each said glass member including at least one strengthened glass portion comprising a stress-engineered glass material; and

an inter-structure bond connected between said first glass member and said second glass member, said inter-structure bond including a bonding member connected between first surface regions of said first and second glass members such that said bonding member is directly connected to at least one weaker member region disposed in at least one of said first and second glass members, said at least one weaker member region comprising a structurally weaker glass material than said stress-engineered glass material of said one or more strengthened glass portions,

wherein said bonding member and said at least one weaker member region are configured to generate a transfer fracture force in response to a first propagating fracture force, said transfer fracture force being directed from said first glass member to said second glass member and having sufficient energy such that secondary propagating fracture forces are generated in said at least one strengthened glass portion of said second glass member.

2. The stress-engineered frangible structure ofclaim 1,

wherein said at least one weaker member region comprises one of a weakened glass portion and a weakened surface feature disposed within a second surface region of the second glass member, and

wherein said bonding member is sandwiched between said first surface regions of the first and second glass members, respectively, such that the first surface region of the second glass member that is contacted by the bonding member entirely surrounds the second surface region surrounding said at least one weaker member region.

3. The stress-engineered frangible structure ofclaim 1,

wherein said at least one weaker member region includes a first weakened glass portion disposed in the first glass member and a second weakened glass portion disposed in the second glass member, and

wherein said inter-structure bond comprises said bonding member sandwiched between said first surface regions of the first and second glass members, respectively, wherein the first surface regions are contiguous with and surround said first and second weakened glass portions.

4. The stress-engineered frangible structure according toclaim 1, further comprising a trigger mechanism operably attached to said first glass member, said trigger mechanism being configured to generate an initial fracture force sufficient to cause said first propagating fracture force in said at least one strengthened portion of said first glass member.

5. The stress-engineered frangible structure according toclaim 4, further comprising a sensor configured to detect a predetermined transmitted wave signal, and configured to generate a trigger signal upon detection of said predetermined transmitted wave signal, wherein said trigger mechanism is further configured to generate said initial fracture force in response to said trigger signal.

6. The stress-engineered frangible structure according toclaim 1, wherein said at least one strengthened portion of said first and second glass members comprises one of a thermally tempered glass material, a laminated glass material, and an ion-exchange treated glass material.

7. A method for producing a stress-engineered frangible structure having a structural shape, the method comprising:

providing a plurality of discrete glass members configured to collectively form, when operably assembled, said structural shape; and

interconnecting said plurality of discrete glass members such that each said discrete glass member is directly connected by way of an associated inter-structure bond to an adjacent one of said discrete glass member,

wherein, after said interconnecting, each said glass member includes at least one strengthened portion comprising a stress-engineered glass material, and

wherein each of said one or more inter-structure bonds is configured to transfer first propagating fracture forces from said at least one strengthened portion of a first said glass member to said at least one strengthened portion of an adjacent second said glass member such that secondary propagating fracture forces are generated in said adjacent second glass member in response to said transferred first propagating forces.

8. The method ofclaim 7, further comprising mounting a trigger mechanism onto said first glass member, said trigger mechanism being configured to generate an initial fracture force in said first glass member, whereby said initial propagating fracture forces generated in said first glass member by said trigger mechanism are transferred by way of said one or more inter-structure bonds to all of said plurality of interconnected glass members.

9. The method ofclaim 8, wherein interconnecting comprises:

generating a weaker member region in the second glass member; and

connecting said first and second glass members such that a bonding member is disposed over said weaker member region.

10. The method ofclaim 9, wherein generating said weaker member region comprises:

providing first and second discrete untreated glass members;

forming a mask over a designated surface region of said second discrete untreated glass member;

subjecting all exposed surfaces of said first and second discrete untreated glass members to an ion-exchange treatment, whereby said first and second untreated glass members are converted into said first and second glass members with said second glass member having a weakened glass portion disposed under said mask;

removing said mask; and

connecting said first and second glass members such that said bonding member is disposed against said weakened glass portion.

11. The method ofclaim 9, wherein generating said weaker member region comprises:

providing first and second discrete untreated glass members;

subjecting all exposed surfaces of said first and second discrete untreated glass members to an ion-exchange treatment, whereby said first and second untreated glass members are converted into said first and second glass members including said at least one strengthened portion;

forming a weakened surface feature by removing glass material from said at least one strengthened portion of the second glass member through a designated surface region; and connecting said first and second glass members such that said bonding member is disposed against said weakened surface feature.

12. The method ofclaim 11, wherein forming said weakened surface feature comprises etching said designated surface region to define one of a single cavity, a plurality of adjacent cavities, and one or more slots through said designated surface region into said second glass member.

13. The method ofclaim 9, wherein connecting said first and second glass members comprises applying one of a ceramic adhesive, a low temperature glass frit, an anodic bonding structure, and a chemical bond.

14. The method ofclaim 7, wherein the step of interconnecting comprises:

providing first and second discrete untreated glass members;

forming a first said inter-structure bond by connecting a first designated surface bonding region of said first untreated glass member to a second designated surface region of said second discrete untreated glass member by way of an intervening glass bonding member, whereby said first inter-structure bond includes said glass bonding member, a first weakened glass portion disposed in said first untreated glass member adjacent to said first designated surface region, and a second weakened glass portion disposed in said second untreated glass member adjacent to said second designated surface region; and

subjecting exposed portions of said first and second discrete untreated glass members to an ion-exchange treatment such that said first and second untreated glass members are converted into said first and second glass members connected by said first inter-structure bond.

15. The method ofclaim 14,

wherein providing said first and second discrete untreated glass members comprises providing glass materials having the same or similar coefficients of thermal expansion; and

wherein forming said first inter-structure bond comprises utilizing a high temperature glass bonding technique.

16. The method ofclaim 14, wherein said connecting comprises forming said intervening glass bonding member using a high-temperature glass frit.

17. The method ofclaim 14, further comprising forming channels in exposed surface portions of said first and second discrete untreated glass members before said subjecting exposed portions of said first and second discrete untreated glass members to said ion-exchange treatment.

18. A method for producing a frangible structure in which propagating fracture forces are transferable in only one direction between first and second glass members, the method comprising:

generating strengthened glass portions in said first and second glass members, and a weaker member region in said second glass member;

interconnecting said first and second glass members such that a bonding member is directly connected between said weaker member region of said second glass member and said strengthened glass portion of said first glass member; and

mounting a trigger mechanism onto said first glass member, said trigger mechanism being configured to generate initial propagating fracture forces in said first glass member, whereby said initial propagating fracture forces generated in said first glass member by said trigger mechanism are transferred by way of said bonding member and said weaker member region to said second glass member.

19. The method ofclaim 18,

wherein generating said weaker member region comprises generating one of a weakened glass portion and a weakened surface feature in said second glass member, and

wherein interconnecting said first and second glass members comprises disposing said bonding member over said one of said weakened glass portion and said weakened surface feature.

20. The method ofclaim 19, wherein generating said weakened surface feature comprises:

providing an untreated glass member;

subjecting all exposed surfaces of said untreated glass member to an ion-exchange treatment, whereby said untreated glass member is converted into said second glass member having said weakened glass portion located under said mask; and

forming said weakened surface feature by removing glass material from said weakened glass portion through said designated surface region.

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